The objectives of the proposed project are: 1. To develop the necessary instrumentation and techniques to utilize electron energy loss spectroscopy as an important complement to X-ray spectroscopy for the elemental microanalysis of biological material. Then, through this development, to utilize the increased sensitivity of the energy loss technique (particularly for low Z, biological materials) to detect smaller elemental concentrations and/or to obtain higher spatial resolution in the microanalysis of biological material than would be possible with X-ray techniques alone. 2. To apply the electron energy loss microanalysis technique to the specific problem of the subcellular localization of the major ions playing a role in excitation and contraction in myocardial cells. A magnetic sector electron spectrometer and parallel data collection system will be constructed and used in conjunction with an energy dispersive X-ray detection system to determine local elemental concentrations in myocardium at subcellular levels. In particular, intracellular concentration of Na, K and Ca 2 ions will be measured in various steady states of muscle and, by using rapid freezing, during various states of excitation and contraction. The proposed research should provide important information concerning myocardial cation distributions and also assess the usefulness and limitations of the energy loss microanalysis technique. It should thus serve as a guide for future investigations using energy loss microanalysis in both normal and diseased tissue.